Reaction Moments Research Articles

Prediction of gait kinetics using Markerless-driven musculoskeletal modeling

Video-based motion analysis systems are emerging in the biomechanics research community, yet there is limited exploration of kinetics prediction using RGB-markerless kinematics and musculoskeletal modeling. This project aimed to provide ground reaction force (GRF) and ground reaction moment (GRM) predictions during over-ground gait by introducing RGB-markerless kinematics into a musculoskeletal modeling framework. Full-body markerless kinematic inputs and musculoskeletal modeling were used to obtain GRF and GRM predictions which were compared to measured force plate values. The markerless-driven predictions yielded average root mean-squared error (RMSE) in the stance phase of 0.035 ± 0.009 N∙BW−1, 0.070 ± 0.014 N∙BW−1, and 0.155 ± 0.041 N∙BW−1 in the mediolateral (ML), anteroposterior (AP), and vertical (V) GRFs. This was accompanied by moderate to high correlations and interclass correlation coefficients (ICC) indicating moderate to good agreement between measured and predicted values (95% Confidence Inervals: ML = [0.479, 0.717], AP = [0.714, 0.856], V = [0.803, 0.905]). For ground reaction moments (GRM), average RMSE was 0.029 ± 0.013 Nm∙BWH-1, 0.014 ± 0.005 Nm∙BWH-1, and 0.005 ± 0.002 Nm∙BWH-1 in the sagittal, frontal, and transverse planes. Pearson correlations and ICCs indicated poor agreement between systems for GRMs (95% Confidence Intervals: Sagittal = [0.314, 0.608], Frontal = [0.006, 0.373], Transverse = [0.269, 0.570]). Currently, RMSE is larger than target thresholds set from studies using Kinect, inertial, or marker-based kinematic drivers; but methodological considerations highlighted in this work may help guide follow-up iterations. At this point, further use in research or clinical practice is cautioned until methodological considerations are addressed, although results are promising at this point.

Three-Dimensional Force Characterizations in Maxillary Molar Distalization: A Finite Element Study

Class II malocclusion is a very common condition in orthodontic patients. The reaction force and moment on the teeth induced by a maxillary segmental distalizer (MSD) are essential for understanding tooth movement, tipping, and rotation. This work quantified the three-dimensional (3D) reaction force and moment on canine and molar teeth induced by three different MSDs: the JVBarre (JVB), Carriere Motion 3D (CM3D), and CM3D Clear. A patient-specific mandibular model was reconstructed based on cone-beam computed tomography (CBCT) images. Each of the three MSDs was implanted using finite element analysis (FEA). The reaction force and moment were obtained. The results show that the JVB induced less extrusion force (15% less), tipping (90% less), and rotational moment (70% less) on the canine, compared with the other two CM3Ds. However, the JVB induced a relatively larger extrusion force, tipping, and rotational moment on the molar due to the hook location changing from the end to the middle of the bar. These observations were consistent with the 3D stress distribution of the MSDs. The mechanical understanding from this work may shed light on the optimal design of MSDs.

Design of bionic prosthetic leg

Along with the increase in the number of Indonesian people who are physically disabled and the number of cases of leg amputations above the knee, the need for prosthetic limbs in Indonesia is also increasing. Prosthetic limbs are tools to replace lost limbs caused by birth defects, amputations, or disease. The bionic prosthetic leg has a long-term useful purpose, as well as supporting the rights of people with disabilities. The device helps the above-the-knee amputee. To design a bionic prosthetic leg, a biomechanical analysis of work is needed to obtain a walking pattern in humans and an analysis of the structure and working material to obtain a safe and comfortable material for use in a bionic prosthetic foot. This bionic leg prosthetic uses an automatic system using an Electromyography (EMG) sensor as a signal picker for the muscles, Arduino Mega 2560 as an input signal processor which is then converted into an output signal and Planetary gear as a knee joint transmission so that the body does not fall forward or backward. The results of the analysis using Autodesk Inventor software on the prosthetic of the bionic leg can withstand a pressure of 404.526 MPa, withstand a reaction force of 354.576 N and a reaction moment of 15.4073 N. So based on the results of the bionic prosthetic leg is very safe and comfortable when used on people with disabilities.

A prophylactic lumbosacral brace and the biomechanics of parachute landing.

Lumbar injuries are common among paratroopers during landing maneuvers. Although bracing is widely advocated to increase spine stability, the effect of lumbar bracing on parachuting has yet to be quantified and the Chinese parachutist does not have a uniform prophylactic brace. The aim is to compare the effects of a novel, self-designed and self-manufactured lumbosacral brace with two ordinary lumbar braces based on biomechanical assessment of the lumbar and lower extremity joints during parachute landing. The study cohort consisted of 30 elite male paratroopers. Each participant was instructed to jump off a platform at two different heights (60 and 120 cm, respectively) and land on the force plate in a half-squat posture. Participants at each height were tested under four different conditions (no brace, elastic brace, semi-rigid brace, and lumbosacral brace). The Vicon 3D motion capture system and force plate were used to record and calculate biomechanical data, such as vertical ground reaction forces (vGRFs), joint angles, moments, and energy absorption. After the experiment, every participant completed the study questionnaires. The increase of the jumping height raised all the parameters significantly (P<0.01). The use of all three braces slightly decreased vGRF, and reduced the lumbar angle, moment, and angular velocity in the sagittal plane. The use of lumbosacral and semi-rigid braces restricted lumbar flexion more efficiently (P<0.05), and significantly increased the energy absorption of the hip joints (P<0.01) and hip flexion (P<0.01) at 120 cm. No significant effect of braces was found on the motion of knee and ankle joints. The subjective scores suggested that the lumbosacral brace was softer and more comfortable than the semi-rigid brace, and more effective than the elastic brace. The lumbosacral brace markedly restricted the lumbar motion in the sagittal plane than the elastic brace and was more comfortable than the semi-rigid brace. Therefore, the innovative design, high efficiency, and comfortable landing of the lumbosacral brace represent a reliable option for parachute jumping and training.

Pelvis perturbations in various directions while standing in staggered stance elicit concurrent responses in both the sagittal and frontal plane.

Increasing knowledge on human balance recovery strategies is important for the development of balance assistance strategies using assistive devices like a powered lower-limb exoskeleton. One of the postures which is relevant for this scenario, but underexposed in research, is staggered stance, a posture with one foot in front. We therefore aimed to gain a better understanding of balance recovery in staggered stance. We studied balance responses at joint- and muscle levels to pelvis perturbations in various directions while standing in this posture. Ten healthy individuals participated in this study. We used one actuator beside and one behind the participant to apply 150 ms perturbations in mediolateral (ML), anteroposterior (AP) and diagonal directions, with a magnitude of 3, 6, 9 and 12% of the participant's body weight (BW). Meanwhile, motion capture, ground reaction forces and moments, and electromyography of the muscles around the ankles and hips were recorded. The perturbations caused movements of the centre of mass (CoM) and centre of pressure (CoP) in the direction of the perturbation. These were often accompanied by motions in a direction different from the perturbation direction. After perturbations perpendicular to the line between both feet, large and significant AP deviations were present of the CoM (-0.27 till 0.40 cm/%BW, p < 0.029) and CoP (-0.99 till 0.80 cm/%BW, p < 0.001). Also, stronger responses on joint and muscle level were present after these perturbations, compared to AP and diagonal perturbations collinear with the line between both feet. The hip, knee and ankle joints contributed differently to the balance responses after the different perturbation directions. To conclude, standing in a staggered stance posture makes individuals more vulnerable to perturbations perpendicular to the line between both feet, requiring larger responses on joint level as well as contributions in the sagittal plane.

A dataset of asymptomatic human gait and movements obtained from markers, IMUs, insoles and force plates

Human motion capture and analysis could be made easier through the use of wearable devices such as inertial sensors and/or pressure insoles. However, many steps are still needed to reach the performance of optoelectronic systems to compute kinematic parameters. The proposed dataset has been established on 10 asymptomatic adults. Participants were asked to walk at different speeds on a 10-meters walkway in a laboratory and to perform different movements such as squats or knee flexion/extension tasks. Three-dimensional trajectories of 69 reflective markers placed according to a conventional full body markerset, acceleration and angular velocity signals of 8 inertial sensors, pressure signals of 2 insoles, 3D ground reaction forces and moments obtained from 3 force plates were simultaneously recorded. Eight calculated virtual markers related to joint centers were also added to the dataset. This dataset contains a total of 337 trials including static and dynamic tasks for each participant. Its purpose is to enable comparisons between various motion capture systems and stimulate the development of new methods for gait analysis.

Roles of each leg in impulse generation in professional baseball pitchers: preliminary findings uncover the contribution of the back leg towards whole-body rotation

ABSTRACT This study examined the roles of each leg in generating linear and angular impulses during baseball pitching. Professional pitchers (n = 4) pitched from a force plate instrumented mound, and 6–11 successful fastball pitches were used for analyses. We compared linear and angular impulses across the back and front legs. Linear and angular impulses were calculated from ground reaction force (GRF) and moment about each global axis passing through the centre of mass (COM), respectively. Additionally, we analysed measures that control the moment: (1) GRF magnitude, (2) magnitude of the position vector from COM to the centre of pressure and (3) the angle between (1) and (2). We found that the back leg generated forward linear impulse and the front leg generated backward linear impulse for all pitchers. Surprisingly, we found that the back leg generated significantly greater positive angular impulse about a global leftward axis (from the mound towards first base) than did the front leg in all four pitchers. Furthermore, the back leg’s moment about the leftward axis became positive after the magnitude of forward GRF decreased from its maximum, suggesting that the back leg’s role transitioned from generating forward linear momentum to angular momentum.

Coupled Chemo-Mechanical Swelling Behavior of PH-Sensitive Hollow Cylinder Hydrogels under Extension–Torsion and Internal Pressure: Analytical and 3D FEM Solutions

The coupled transient chemo-mechanical behavior as well as the large deformation behavior under various complex load conditions must be taken into account when designing a functional responsive polymer actuator or sensor. One sort of deformation that can be used to characterize the properties of materials with complicated behavior, like soft hydrogels, is coupled extension and torsion with internal pressure. It is important to thoroughly research the complex kinetics of pH-hydrogels with coupled diffusion and massive deformation behavior. The transient behavior of cylindrical hydrogels under coupled extension–torsion with internal pressure under indifferent conditions is proposed in this work using a reliable semi-analytical method. In this regard, an analytical solution is offered to inspect this problem, which is used as a common experimental methodology for the characterization and modeling of polymeric materials. The results show that the rate of deformation and the physical characteristics of the material have a substantial impact on the cylindrical hydrogel’s transient behavior under coupled extension–torsion and internal pressure. For the same problem, a 3D finite element study was done to assess the analytical solution. The accuracy of our method is supported by the results’ agreement in both the FE analysis and the proposed approach. However, offering such a solution for this complex problem is of tremendous relevance given the significantly cheaper computational cost of analytical methods when compared to FEM. Additionally, the calculations indicate a complex reaction force and moment because the hydrogel experiences nonlinear Poynting-type effects in this deformation domain. The suggested semi-analytical procedure’s resilience behavior is demonstrated by the visualization of the effects of various material properties. This method can be used to calibrate constitutive models and to develop and improve hydrogel structures.

Prediction of ground reaction forces and moments during walking in children with cerebral palsy.

Gait analysis is increasingly used to support clinical decision-making regarding diagnosis and treatment planning for movement disorders. As a key part of gait analysis, inverse dynamics can be applied to estimate internal loading conditions during movement, which is essential for understanding pathological gait patterns. The inverse dynamics calculation uses external kinetic information, normally collected using force plates. However, collection of external ground reaction forces (GRFs) and moments (GRMs) can be challenging, especially in subjects with movement disorders. In recent years, a musculoskeletal modeling-based approach has been developed to predict external kinetics from kinematic data, but its performance has not yet been evaluated for altered locomotor patterns such as toe-walking. Therefore, the goal of this study was to investigate how well this prediction method performs for gait in children with cerebral palsy. The method was applied to 25 subjects with various forms of hemiplegic spastic locomotor patterns. Predicted GRFs and GRMs, in addition to associated joint kinetics derived using inverse dynamics, were statistically compared against those based on force plate measurements. The results showed that the performance of the predictive method was similar for the affected and unaffected limbs, with Pearson correlation coefficients between predicted and measured GRFs of 0.71-0.96, similar to those previously reported for healthy adults, despite the motor pathology and the inclusion of toes-walkers within our cohort. However, errors were amplified when calculating the resulting joint moments to an extent that could influence clinical interpretation. To conclude, the musculoskeletal modeling-based approach for estimating external kinetics is promising for pathological gait, offering the possibility of estimating GRFs and GRMs without the need for force plate data. However, further development is needed before implementation within clinical settings becomes possible.

Exoskeletons need to react faster than physiological responses to improve standing balance.

Maintaining balance throughout daily activities is challenging because of the unstable nature of the human body. For instance, a person's delayed reaction times limit their ability to restore balance after disturbances. Wearable exoskeletons have the potential to enhance user balance after a disturbance by reacting faster than physiologically possible. However, "artificially fast" balance-correcting exoskeleton torque may interfere with the user's ensuing physiological responses, consequently hindering the overall reactive balance response. Here, we show that exoskeletons need to react faster than physiological responses to improve standing balance after postural perturbations. Delivering ankle exoskeleton torque before the onset of physiological reactive joint moments improved standing balance by 9%, whereas delaying torque onset to coincide with that of physiological reactive ankle moments did not. In addition, artificially fast exoskeleton torque disrupted the ankle mechanics that generate initial local sensory feedback, but the initial reactive soleus muscle activity was only reduced by 18% versus baseline. More variance of the initial reactive soleus muscle activity was accounted for using delayed and scaled whole-body mechanics [specifically center of mass (CoM) velocity] versus local ankle-or soleus fascicle-mechanics, supporting the notion that reactive muscle activity is commanded to achieve task-level goals, such as maintaining balance. Together, to elicit symbiotic human-exoskeleton balance control, device torque may need to be informed by mechanical estimates of global sensory feedback, such as CoM kinematics, that precede physiological responses.

Reaction moments matter when designing lower-extremity robots for tripping recovery.

Balance recovery after tripping often requires an active adaptation of foot placement. Thus far, few attempts have been made to actively assist forward foot placement for balance recovery employing wearable devices. This study aims to explore the possibilities of active forward foot placement through two paradigms of actuation: assistive moments exerted with the reaction moments either internal or external to the human body, namely 'joint' moments and 'free' moments, respectively. Both paradigms can be applied to manipulate the motion of segments of the body (e.g., the shank or thigh), but joint actuators also exert opposing reaction moments on neighbouring body segments, altering posture and potentially inhibiting tripping recovery. We therefore hypothesised that a free moment paradigm is more effective in assisting balance recovery following tripping. The simulation software SCONE was used to simulate gait and tripping over various ground-fixed obstacles during the early swing phase. To aid forward foot placement, joint moments and free moments were applied either on the thigh to augment hip flexion or on the shank to augment knee extension. Two realizations of joint moments on the hip were simulated, with the reaction moment applied to either the pelvis or the contralateral thigh. The simulation results show that assisting hip flexion with either actuation paradigm on the thigh can result in full recovery of gait with a margin of stability and leg kinematics closely matching the unperturbed case. However, when assisting knee extension with moments on the shank, free moment effectively assist balance but joint moments with the reaction moment on the thigh do not. For joint moments assisting hip flexion, placement of the reaction moment on the contralateral thigh was more effective in achieving the desired limb dynamics than placing the reaction on the pelvis. Poor choice of placement of reaction moments may therefore have detrimental consequences for balance recovery, and removing them entirely (i.e., free moment) could be a more effective and reliable alternative. These results challenge conventional assumptions and may inform the design and development of a new generation of minimalistic wearable devices to promote balance during gait.

A proper sequence of dynamic alignment in transtibial prosthesis: insight through socket reaction moments

Dynamic alignment in prosthetic fitting is important because it affects the user’s stability, kinematics, and kinetics such as socket reaction moments. It is performed by tuning the spatial relationship between the transtibial prosthetic socket and the foot following sequential observational gait analysis in the three anatomical planes. However, the order of planes in which the adjustment should be performed is still unclear. To investigate the appropriate sequence of dynamic alignment adjustment, ten participants with transtibial amputation were asked to walk in different alignment conditions (flexion, extension, adduction, abduction; lateral, medial, anterior, and posterior translation of the socket, and plantarflexion, dorsiflexion, inversion, and eversion of the foot) to measure socket reaction moments in the out-of-planes (e.g., the effect of sagittal alignment on the coronal moment). A significant difference was found only among socket posterior translation, socket flexion, and baseline alignment in the coronal moment (P = 0.02). The results of the current and previous studies suggest that moments in the coronal plane are affected by alignment changes in all three planes, whereas moments in the sagittal plane are affected only by sagittal alignment changes. It is suggested that the procedure of alignment adjustments should be finalized in the coronal plane.

Structural layout and operating parameters for a large rotor of a direct-flow bucket wheel type aggregator

Introduction. The problem of accelerating and cheapening the construction of roads without reducing their quality can be solved by creating a complex of continuous units. Units, following each other, carry out the whole complex of works aimed at the construction of roads. The use of satellite navigation opens up broad prospects for full automation of units. Therefore, the overall goal is to create a complex of units that carry out the continuous construction of roads, mainly in automatic mode. One of the devices that make up the continuous units is a direct-flow bucket wheel type aggregator. The use of direct-flow bucket wheel type aggregators for soil development is constrained by insufficient theoretical substantiation of their parameters. Before analyzing the interaction of the elements of the working bodies of a direct-flow bucket wheel type aggregator with the soil, it is necessary to clarify the structural layout for the rotor of a direct-flow bucket wheel type aggregator.The method of research. Some design parameters of a direct-flow bucket wheel type aggregator are derived from logical reasoning. Other parameters of the direct-flow bucket wheel type aggregator are obtained by constructing schemes for the impact of the knife on the ground in the plane and spatial modelling. Initially, the rotor of a direct-flow bucket wheel type aggregator with a diameter of one meter was adopted for calculation.Results. The circular and end knives are assigned the numbers № 1, № 2, № 3, etc. as it approaches from the periphery of the rotor to the axis of its rotation. On the basis of the adopted methodology, the design of the knife attachment, the front and back corner of the circular and end knives have been clarified. An extremely small distance from the axis of rotation of the rotor to the nearest point of the knife is established. Hence the conclusion is made that in addition to a large rotor, in conjunction with it, it is necessary to install a small rotor. The circumferential velocity of the blade of no. 1 circumferential knife and the angular velocity of the large rotor are determined. It is customary to arrange the knives in three rows, that is, the rows of knives around the circumference are deployed at an angle of 120° relative to each other. The feed on the end knife was revealed, that is, the thickness of the layer cut by the end knife.Conclusion. On the basis of the adopted methodology, the geometric and mode parameters of a large rotor of a direct-flow bucket wheel type aggregator have been determined. An extremely small radius of location of the circular and end knives of the large rotor is established. To excavate the soil near the axis of rotation for the rotor of the direct-flow bucket wheel type aggregator, a small rotor with a higher angular velocity shall be coaxially installed. The direction of rotation of the small rotor shall be opposite to the direction of rotation of the large rotor in order to partially compensate for the reactive moment produced by the large rotor.

Ground Reaction Force and Moment Estimation through EMG Sensing Using Long Short-Term Memory Network during Posture Coordination

Motion prediction based on kinematic information such as body segment displacement and joint angle has been widely studied. Because motions originate from forces, it is beneficial to estimate dynamic information, such as the ground reaction force (GRF), in addition to kinematic information for advanced motion prediction. In this study, we proposed a method to estimate GRF and ground reaction moment (GRM) from electromyography (EMG) in combination with and without an inertial measurement unit (IMU) sensor using a machine learning technique. A long short-term memory network, which is suitable for processing long time-span data, was constructed with EMG and IMU as input data to estimate GRF during posture control and stepping motion. The results demonstrate that the proposed method can provide the GRF estimation with a root mean square error (RMSE) of 8.22 ± 0.97% (mean ± SE) for the posture control motion and 11.17 ± 2.16% (mean ± SE) for the stepping motion. We could confirm that EMG input is essential especially when we need to predict both GRF and GRM with limited numbers of sensors attached under knees. In addition, we developed a GRF visualization system integrated with ongoing motion in a Unity environment. This system enabled the visualization of the GRF vector in 3-dimensional space and provides predictive motion direction based on the estimated GRF, which can be useful for human motion prediction with portable sensors.

Computational wind–structure interaction simulations of high rise and slender structures and validation against on-site measurements — Methodology development and assessment

This contribution proposes a high-fidelity simulation approach for high-rise and slender structures in wind and a suitable validation strategy of the wind–structure interaction computations against on-site measurements instead of comparing to scaled wind-tunnel measurements. Concerning the level of abstraction and modeling in simulation, one usually distinguishes between low- and high-fidelity simulations. Thus, the term fidelity expresses the degree to which the details of the real-world scenario are represented in the numerical simulation model. As a consequence, a high-fidelity approach, as it is elaborated in this contribution, can provide very detailed insights.Whereas the developed procedures are rather general, all steps are demonstrated at the example of the Olympic Tower in Munich, in order to prove their applicability for complex real-world problems and especially to highlight the respective challenges and relevance of certain aspects in modeling, simulation and validation. This holistic simulation and validation approach contains many linked aspects and it is thus presented stepwise as follows.In a first step, the numerical methodology is shortly presented, which inherits the finite element formulations for modeling the fluid flow and the structure in up to a very high level of fidelity. Additionally, the coupling methodology and the mapping operation for the partitioned wind–structure coupling approach is introduced.In a second step, the main characteristics of the structural system of the Olympic Tower in Munich and the measured turbulent wind field are presented. Within the numerical simulation, the respective wind field is realized via a synthetic inlet generator.This wind field was validated against the wind characteristics available from the on-site measurements before being further applied to the coupled wind–structure interaction simulations. Furthermore, convergence studies and validation simulations for the single subproblems, i.e. fluid flow and structural dynamics, are presented.In a third step, the results of the wind–structure interaction simulations, which are conducted in real scale, are presented. Those contain, besides some convergence studies and validation of the fluid flow results, the comparison of the tower’s reaction moments in the lateral and longitudinal direction to the on-site measurements. This comparison shows good accordance between simulated and on-site measured values while identifying possible deficiencies in the measurement methodology, thus demonstrating the potentials of Computational Wind Engineering approaches for assessment of wind-induced transient effects of slender high-rise structures in complex atmospheric-boundary-layer flows.

An investigation into the hammer toe effects on the lower extremity mechanics and plantar fascia tension: A case for a vicious cycle and progressive damage

Hammer toes are one of the common deformities of the forefoot that can lead to compensatory changes during walking in individuals with this condition. Predicting the adverse effects of tissue damage on the performance of other limbs is very important in the prevention of progressive damage. Finite element (FE) and musculoskeletal modeling can be helpful by allowing such effects to be studied in a way where the internal stresses in the tissue could be investigated. Hence, this study aims to investigate the effects of the hammer toe deformity on the lower extremity, especially on the plantar fascia functions. To compare the joint reactions of the hammer toe foot (HTF) and healthy foot (HF), two musculoskeletal models (MSM) of the feet of a healthy individual and that of a participant with hammer toe foot were developed based on gait analysis. A previously validated 3D finite element model which was constructed using Magnetic Resonance Imaging (MRI) of the diabetic participant with the hammer toe deformity was processed at five different events during the stance phase of gait.It was found that the hammer toe deformity makes dorsiflexion of the toes and the windlass mechanism less effective during walking. Specifically, the FE analysis results showed that plantar fascia (PF) in HTF compared to HF played a less dominant role in load bearing with both medial and lateral parts of PF loaded. Also, the results indicated that the stored elastic energy in PF was less in HTF than the HF, which can indicate a higher metabolic cost during walking. Internal stress distribution shows that the majority of ground reaction forces are transmitted through the lateral metatarsals in hammer toe foot, and the probability of fifth metatarsal fracture and also progressive deformity was subsequently increased. The MSM results showed that the joint reaction forces and moments in the hammer toe foot have deviated from normal, where the metatarsophalangeal joint reactions in the hammer toe were less than the values in the healthy foot. This can indicate a vicious cycle of foot deformity, leading to changes in body weight force transmission line, and deviation of joint reactions and plantar fascia function from normal. These in turn lead to increased internal stress concentration, which in turn lead to further foot deformities. This vicious cycle cause progressive damage and can lead to an increase in the risk of ulceration in the diabetic foot.

Dynamic analysis of a translating five-bar linkage mechanism

In this paper, the dynamic analysis of a translating five-bar linkage mechanism is presented. The dynamic model of the mechanism is developed with the applied force to the crank arm resolved into the two principal planes, that is, x- and y- directions and the resulting reaction forces and moments at the pin joints determined at various translating acceleration of 0, 10, 20, 30 and 40 m/s2 in the direction as well as in the opposite direction of the crank rotation. It was observed that the horizontal reaction forces at the pin joints were decreasing as the translating acceleration increases in the direction of crank rotation while it increases when the acceleration increases in the opposite direction to the crank rotation. It was also observed that the pin joint moments at point A decreases as the translation velocities increases in the crank arm rotation direction while it increases as the acceleration increases in the opposite direction. The converse is the case for pin joint B, while there were no significant differences for pin joint moments at pin joints C and D in all the considered acceleration in both directions. Also, the vertical reaction forces at the pin joints did not change in magnitude as the magnitude and directions of the acceleration were altered. The analysis brings to the fore the importance of the consideration of translating acceleration in the design, development and utilization of five – bar linkage to avoid failure at any of the joints.

A Novel Heat-Assisted Three-Roll Incremental Rolling System for Flexible Rolling

Abstract The increasing demand for customized products and rapid prototyping triggers the development of dieless forming process where the need of part-specific dies is eliminated compared to conventional forming processes. This paper presents a heat-assisted three-roll incremental rolling system capable of producing rods and tubes of various diameters without the need for die/tool replacement. The system incorporates two possible heating mechanisms, namely, an induction heater and a high-current power supply for electrically assisted forming. Due to its high flexibility and hot forming ability, this rolling system is ideal for low volume production or scientific research. The newly fabricated rolling machine was initially evaluated using low carbon steel rods. The experiments have shown that the machine can produce metallic rods down to 6 mm in diameter without apparent spiral marks on the outer surface of the rolled product using multiple passes. The finite element method (FEM) was used to analyze the reaction moment, depth of the spiral marks, and the effect of axial feeding speed on the spiral marks. The simulation model predicted the results of the experiments with less than a 10% error. The work established a flexible rolling platform for possible future research, which can include the study of interface behavior in the thermo-mechanical rolling processes, and the study of material behavior in this multi-axial multi-physics environment.

A biomechanical analysis of dumbbell curl and investigation of the effects of increasing loads on biceps brachii using a finite element model

Dumbbell curl is one of the most important strengthening exercises for the upper extremity. This exercise trains especially biceps brachii. Exercise load is increased to achieve more muscle strength for the biceps brachii. Researchers are usually focused on electromyography (EMG) in order to examine the effects of load increasing on muscle contraction. However, only the muscle force can be predicted with EMG measurement. Structural analysis of the muscles cannot be performed. In this study, the effects of load increasing on biceps brachii were investigated by mechanical analysis. The inverse dynamic model was simulated according to the motion analysis of dumbbell curl exercises performed with 6 kg and 10.7 kg. The muscle force of the biceps brachii was calculated from the elbow joint reaction moment. A simplified finite element model of biceps brachii was created and stress-strain response was examined. Although the muscle force increases by 78.3%, the rate of increase of elbow peak moment is 57.7% and the rate of increase of peak muscle force is 38.3%. Similarly, the rate of increase of maximum strain and maximum stress are 44.4% and 37.3%, respectively. According to these results, it is understood that increasing the dumbbell load does not increase the muscle force at the same rate.

Locomotion control during curb descent: Bilateral ground reaction variables covary consistently during the double support phase regardless of future foot placement constraints.

During community ambulation, anticipatory adaptations in gait are key for navigating built, populated and natural environments. It has been argued that some instability in gait can be functionally beneficial in situations demanding high maneuverability, and while the mechanisms utilized to maintain locomotor balance are well understood, relatively less is known about how the control of gait stability changes to facilitate upcoming maneuvers in challenging environments. The double support phase may be important in this regard; since both feet can push off the ground simultaneously, there is greater control authority over the body's movement during this phase. Our goal was to identify how this control authority is exploited to prepare for upcoming maneuvers in challenging environments. We used synergy indices to quantify the degree of coordination between the ground reaction forces and moments under the two feet for stabilizing the resultant force and moment on the body during the double support phase of curb descent. In contrast to our expectations, we observed that the kinetic synergy indices during curb descent were minimally influenced by expected foot targeting maneuvers for the subsequent step. Only the resultant moment in the frontal plane showed reduced stability when targeting was required, but the synergy index was still high, indicating that the resultant moment was stable. Furthermore, the synergy indices indicated that the main function of the ground reaction variables is to maintain stability of whole-body rotations during double support, and this prerogative was minimally influenced by the subsequent foot targeting tasks, likely because the cost of losing balance while descending a curb would be higher than the cost of mis-stepping on a visual target. Our work demonstrates the salience of stabilizing body rotations during curb negotiation and improves our understanding of locomotor control in challenging environments.